JP3214063B2 - Hologram interferometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram interferometer for measuring the state of the surface of an object to be measured.

[0002]

2. Description of the Related Art In order to measure the surface shape of a lens or another object to be measured, a reference lens serving as a reference of a lens as an object to be measured is used, and interference fringes are generated between the reference lens and the object to be measured. And observing this interference fringe,
The surface finishing accuracy of the test object can be measured. Further, an interferometer is used to measure the reference lens and the test object in a non-contact manner. There are various types of interferometers. Among them, the Fizeau-type interferometer is applied in a wide field because of its advantages such as its simple structure. This Fizeau interferometer uses a laser light source, converts a laser beam emitted from the laser light source into a parallel light beam, irradiates the parallel light beam onto a reference lens, partially reflects the light onto the reference surface of the reference lens, The light transmitted through the lens is reflected by the test surface of the test object, and the interference between the reference wave light from the reference surface of these reference lenses and the object wave light from the test surface of the test object is exhibited. The interference fringes are displayed on a monitor screen or the like to observe the interference fringes.

In recent years, a hologram interferometer for measuring the surface state of a test object by using a computer-generated hologram has been put to practical use. This type of hologram interferometer uses a hologram optical element instead of using a reference lens as in the Fizeau interferometer described above. The hologram optical element was formed by applying a photoresist film on a glass substrate, and scanning the photoresist film with an electron beam, thereby exposing an interference fringe pattern equivalent to the interference fringe pattern between the object wave light and the reference wave light. Then, the optical element is developed to develop interference fringes. When the same reproduction wave as the reference wave light enters the interference fringes in the hologram optical element, the object wave light can be reproduced. According to the interferometry using this hologram, inspection and measurement of a special shape are possible, so that it is expected to be widely used in the future.

[0004]

The present applicant has proposed a hologram interferometer having the structure shown in FIG. In the figure, 1 is a laser light source, 2 is a diverging lens,
Reference numerals 3 denote pinholes, respectively. A laser beam emitted from the laser light source 1 is condensed by a diverging lens 2, and after passing through the pinhole 3 disposed at the condensing position, irradiates the beam splitter 4 while diverging. Then, the light is reflected by the beam splitter 4 and the optical path is bent by 90 °. The laser light flux diverged by the pinhole 3 is
After being reflected by the beam splitter 4, it is converted into a parallel light beam by the collimator lens 5 and is incident on the hologram optical element 6. When the laser beam is incident on the hologram optical element 6, the laser beam is divided into regular reflected light and diffracted light. In the optical path of the regular reflection light, a reference reflection plate 7 having a reference reflection surface 7a perpendicular to the regular reflection light is provided.

On the other hand, a test object 8 is arranged in the optical path of the diffracted light. Here, assuming that the test object 8 is a cylindrical lens, the hologram pattern of the hologram optical element 6 is a stripe pattern arranged in parallel straight lines. Then, the direction of the stripe of the hologram optical element 6 is
Are arranged in the direction of the generatrix of the cylindrical surface 8a at a position where the diffracted light is condensed on the central axis.

[0006] A laser beam from the laser light source 1 passes through a diverging lens 2 and a pinhole 3 constituting a light transmitting optical system, is reflected by a beam splitter 4 and is converted into a parallel beam by a collimator lens 5. Is incident on the hologram optical element 6. The diffracted light from the hologram optical element 6 is once condensed at a position on the central axis of the cylindrical surface 8a of the test object 8, diverges, irradiates the cylindrical surface 8a, and is reflected by the cylindrical surface 8a. Then, the process returns to the hologram optical element 6. The return light from the test object 8 is reflected by the hologram optical element 6 and returns to the collimator lens 5 as original parallel light. on the other hand,
The regular reflection light from the hologram optical element 6 is reflected by the reference reflection surface 7a of the reference reflection plate 7, and the return light is reflected again by the hologram optical element 6 and travels toward the collimator lens 5.

Therefore, the object wave light in the pattern by the hologram optical element 6 overlaps with the reference wave light from the reference reflection plate 7 and interferes with each other to form interference fringes. This light passes through the beam splitter 4 and is collimated by a collimator lens 5.
The interference fringes are formed on the image forming surface of the image pickup means 10 through the image forming lens 9 provided at the rear focal position.

Since the hologram optical element 6 converts the plane wave into an aspherical wave corresponding to the cylindrical surface 8a by the action of the hologram optical element 6, the interference fringes are generated as a result of interference between parallel lights. An extremely clear interference fringe pattern is imaged by the imaging means 10. Accordingly, the shape of the cylindrical surface 8a of the test object 8 can be measured with extremely high accuracy.

In the hologram interferometer described above, if the angle between the light incident on the hologram optical element 6 and the diffracted light is reduced, a more accurate interference fringe pattern can be obtained. Measurement accuracy is also improved. However, a test object 8 is disposed on an extension of the diffracted light, and the test object 8 is required to be positioned at least in the XY directions and the rotational directions in order to perform extremely accurate alignment with the hologram optical element. It is set on a sample table provided on an adjustment table that can be adjusted in position. When an actual measurement is performed, the focus position of the diffracted light from the hologram optical element called the cat's eye position After that, the light-condensing position is moved to a position where the converging position becomes the front focal position of the test object 8. Therefore, if the angle of incidence on the hologram optical element 8 is reduced, there is an inconvenience that the sample path or the like causes the optical path to be blurred.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and ensures that even if the angle of incidence of the laser beam on the hologram optical element is reduced, the optical path is not deviated. It is intended to prevent such problems.

[0011]

In order to achieve the above-mentioned object, the present invention provides a laser beam from a laser light source which is collimated and radiated to a hologram optical element. the inspected object, and each is reflected on the reference reflective plate specularly reflected light, an interferometer system for generating interference fringes between these, the holographic optical element
In order to irradiate the laser beam into a parallel beam
A reflection mirror is provided opposite to the hologram optical element, and
Between the position where the reflecting mirror and the reference reflector are arranged
The hologram optical element at one side and the other
The object to be measured is arranged on one side, and the reflecting mirror and the
Optical path between the optical element and the reference reflector and
An optical path between the hologram optical element and the hologram;
The position where the optical path between the optical element and the test object intersects
The reflection mirror and the base are closer to a side closer to the test object.
A quasi-reflector is placed, and these reflecting mirrors and a reference
Between the hologram optical element and the test object
It is characterized in that it is configured to be separated by an interval that does not interfere with the optical path between them.

[0012]

The laser beam emitted from the laser light source is converted into a parallel beam, reflected by a reflection mirror and incident on a hologram optical element. In this hologram optical element, the incident laser light beam is divided into diffracted light and specularly reflected light, and the diffracted light travels while converging toward the object to be inspected, diverges after passing through the focusing position, and The object is irradiated on the surface to be inspected.
The specularly reflected light is applied to the reference reflection surface while maintaining the state of the parallel light flux. Light reflected from the test object and the reference reflecting surface is reflected on the hologram optical element to generate interference fringes.

Here, the laser beam incident on the hologram optical element is reflected by a reflecting mirror.
Moreover, since the reflection mirror is disposed between the position where the diffracted light from the hologram optical element is condensed and the position where the light incident on the hologram optical element intersects with the diffracted light, the reflection mirror is always covered. The optical path of the light reflected by the reflection mirror adjusts the position of the sample stage on which the object to be inspected is set and the position of the sample stage because the optical path of the light reflected by the reflection mirror is arranged closer to the hologram optical element than the inspection object. There is no danger of being dislodged by a mechanism or the like. In addition, since the cross-sectional area of the optical path becomes small near the converging position of the diffracted light, it can be made closer to the optical axis of the diffracted light, and when the laser beam enters the hologram optical element, the incident angle is reduced. be able to. The reference reflector is configured to irradiate the hologram optical element with light that is specularly reflected. Since the reference reflector is arranged at a position opposite to the optical path of the diffracted light, the regular reflection is performed. The reflected light is not eclipsed.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, FIG. 1 shows the overall configuration of the hologram interferometer device of the present invention. In the figure, reference numeral 30 denotes a laser light source unit, and the laser light source unit 30 includes an interference fringe observation unit 40.
Is built-in. Reference numeral 50 denotes an interferometer main body.

The laser light source section 30 includes a laser light source 31 composed of a laser oscillator, and a reflection mirror 32, a diverging lens 33, a pinhole 34, a beam splitter 35, and a collimator lens 36 that constitute a light transmitting optical system. Further, a pair of reflection mirrors 37 and 38 for routing an optical path are provided at a position in front of the collimator lens 36. As shown in FIG. 2, the laser light source unit 30 is disposed inside the housing 60 except for the reflection mirrors 37 and 38.

The interference fringe observation unit 40 includes the beam splitter 3
Screen 4 provided at a position facing the optical path of transmitted light from 5
1, an interference fringe imaging lens 42 and an imaging means 43 for imaging the interference fringes. This interference fringe observation unit 40
Are also provided in the housing 60 together with the laser light source unit 30.

The interferometer main body 50 includes a first reflecting mirror 5
1, the second reflection mirror 52, and the hologram optical element 5
3 and a reference reflection plate 54 having a reference reflection surface 54a. These members are mounted on a support plate 61. The sample table 56 has a horizontal surface on which the test object 55 is set so that the test object 55 can be set in a stable state without providing a special positioning and holding mechanism. The cylindrical surface 55a, which is the test surface of the object 55, is directed upward, so that the diffracted light from the hologram optical element 53 is irradiated vertically from above. The test object 55 must be set so as to have a strictly predetermined positional relationship with the hologram optical element 53. To enable the position adjustment of the test object 55, the sample table 56 Well-known X
Table 57, which is mounted on a sample table 56 by the XYθ table 57.
Can be adjusted in the horizontal and rotational directions. If the XYθ table 57 is provided with a tilt function for enabling the adjustment of the tilt angle, the position of the test object 55 can be further accurately and finely adjusted.

The XYθ table 57 is mounted on an elevating member 59 that moves up and down along a guide rail 58, and the elevating member 59 converges the surface to be inspected of the object 55 to be diffracted by the hologram optical element 53. It is possible to move between a cat's eye position, which is a position, and a measurement position separated from the cat's eye position by an interval corresponding to the radius of curvature of the curved surface portion of the cylindrical surface 55a of the test object 55.

The laser light flux, which is a parallel light flux guided into the interferometer main body 50, is reflected by the first reflecting mirror 51 and directed downward once, and then the second reflecting mirror 5
2, the second reflecting mirror 5
The light is incident on the hologram optical element 53 provided at a position above the optical element 2 at a predetermined incident angle. When a parallel light beam enters the hologram optical element 53, a part of the light beam is diffracted,
Others are specularly reflected. The sample stage 5
The cylindrical surface 55 of the test object 55 set on 6
Irradiated on the entire surface of a. On the other hand, the specularly reflected light is applied to the reference reflection surface 54a of the reference reflection plate 54 while maintaining the parallel light flux state.

The reflected light from the test object 55 is incident on the hologram optical element 53 through the same optical path as the incident light, and is diffracted into a parallel light flux. Further, the reflected light from the reference reflecting plate 54 is regularly reflected on the hologram optical element 53 while maintaining the state of the parallel light flux. Then, the object wave light from the test object 55 interferes with the reference wave light from the reference reflector 54. The return light having the interference fringes is transmitted to the second mirror 52,
After being introduced from the interferometer main body 50 through the first reflection mirror 51 to the laser light source unit 30 and converged by passing through the collimator 36 in the laser light source unit 30, it is transmitted through the beam splitter 35 to observe interference fringes. The interference fringe is guided to the unit 40 and forms an interference fringe on the imaging unit 43 via the interference fringe imaging lens 42. In order to accurately match the optical path between the laser light source unit 30 and the interferometer main unit 50, for example, the first reflection mirror 51 may be configured to be adjustable in angle.

By the way, setting the interference fringe pattern of the hologram optical element 53 so that the diffracted light has a small angle allows the measurement of the surface shape of the test object 55 with high accuracy. However, the test object 55 is set on a sample table 56 mounted on an XYθ table 57, and the XYθ table 57 is further attached to an elevating member 59. Moreover, the test object 55
In order to measure the surface shape of the sample, the test object 55 is arranged at the measurement position by the ascending / descending means 59. At first, the test object is arranged at the cat's eye position indicated by the imaginary line in FIG. Move to the measurement position. Thereby, the cylindrical surface 55 of the test object 55 is simply
In addition to the measurement of the surface shape of a, the radius of curvature of the cylindrical surface 55a can be measured. The test object 55 and a sample table 56 serving as a supporting mechanism thereof, an XYθ table 57
In addition, it is necessary to prevent the light incident on the hologram optical element 53 from being shaken by the elevating means 59.

Therefore, in order to prevent the light path incident on the hologram optical element 53 from being obstructed and to minimize the angle of incidence on the hologram optical element 53,
A second reflection mirror 52 is provided, and the second reflection mirror 5
2 is disposed between the hologram optical element 53 and the test object 55, and reflects the laser beam therefrom. Thus, it is possible to prevent the incident optical path to the hologram optical element 53 from being blurred. Further, by disposing the reference reflection plate 54 at a position opposite to the second reflection mirror 52 with the optical path of the diffracted light from the hologram optical element 53 interposed therebetween, the optical path of the reference reflection plate 54 may be deviated. Absent. here,
Since the test object 55 can be displaced between the cat's eye position and the measurement position, the position between the hologram optical element 53 and the test object 55 means that the test object 55 is the most holographic optical element 53. And the position between the hologram optical element 53 and the cat's eye position close to.

On the other hand, the second reflection mirror 52 and the reference reflection plate 54 must not interfere with the optical path between the hologram optical element 53 and the test object 55. Therefore, the optical path between the second reflection mirror 52 and the reference reflection plate 54 and the hologram optical element 53 is
The second reflection mirror 52 and the reference reflection plate 54 are provided on the side closer to the test object 55 than the position where the optical path between the third test object 3 and the test object 55 intersects. Thus, the optical path between the hologram optical element 53 and the test object 55 is not cut off.

Further, in the above-described positional relationship, the second
The reflection mirror 52 and the reference reflection plate 54 are brought as close as possible to the condensing position of the diffracted light and close to the optical axis of the diffracted light. Thereby, the incident light from the second reflection mirror 52 to the hologram optical element 53 can be introduced into the hologram optical element 53 at a small angle such as 15 °, for example, and the measurement can be performed with higher accuracy.

As shown in FIG. 3, when the respective reflecting surfaces of the second reflecting mirror 52 and the reference reflecting plate 54 are supported by the holding members 70 and 71, these holding members 70 and 71 are used. Cutouts 70a and 71a are formed in a portion 71 along the optical path of the diffracted light. by this,
The second reflection mirror 51 and the reference reflection plate 54 can be brought close to the diffracted light as much as possible without diffracting the diffracted light.

In the above-described embodiment, the laser light source unit 30, the interference fringe observation unit 40, and the interferometer main body 50 are configured as separate members, but they are provided in an integral housing. It is good also as composition. Also,
The reflection mirrors 32, 37, 38, and 51 are provided to route the laser light flux, and directly convert the laser light from the laser light source 31 to the second light in a parallel light state.
It is not necessary to provide these reflecting mirrors 32, 37, 38 and 51 if the configuration is such that the light is incident on the reflecting mirror 52.

[0027]

As described above, according to the present invention, the converging position of the diffracted light, the optical path of the diffracted light, the incident optical path to the hologram optical element, and the position where the specularly reflected light intersects. Since the reference reflection plate and the reflection mirror for guiding the laser beam to the hologram optical element are arranged at the positions on both sides of the diffracted light, the light incident on the hologram optical element and the reflected light from the hologram optical element are reduced. Various effects such as being not shaken by members constituting the apparatus, reducing the angle of incidence on the hologram optical element, and measuring the surface shape of the test object with higher accuracy can be achieved.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view of a hologram interferometer showing one embodiment of the present invention.

FIG. 2 is a front view of the hologram interferometer device.

FIG. 3 is an external view showing a configuration of a second reflection mirror and a reference reflection plate.

FIG. 4 is a diagram illustrating the principle of a hologram interferometer.

[Explanation of symbols]

 Reference Signs List 30 laser light source part 31 laser light source 35 beam splitter 36 collimator lens 40 interference fringe observing means 50 interferometer main part 51 first reflection mirror 52 second reflection mirror 53 hologram optical element 54 reference reflection plate 55 test object 56 sample table

Claims (1)

(57) [Claims] 1. A irradiated to the holographic optical element is collimated laser light from the laser light source, the diffracted light from the holographic optical element to be examined object, also respectively is reflected on the reference reflective plate specular reflected light In the interferometer device for generating interference fringes between these, the laser beam converted into a parallel light beam by the hologram optical element is
To irradiate the hologram optical element, a reflective mirror
Are disposed facing each other, and the position where the reflection mirror and the reference reflection plate are disposed is
Sandwich the hologram optical element at one side,
The object to be measured is arranged on the other side, and an optical path between the reflection mirror and the hologram optical element is arranged.
And between the reference reflector and the hologram optical element
An optical path, between the hologram optical element and the test object;
Closer to the object than the position where the optical path intersects
The reflection mirror and the reference reflection plate are disposed, and the hologram is provided between the reflection mirror and the reference reflection plate.
Do not interfere with the optical path between the optical element and the test object.
A hologram interferometer device characterized in that the hologram interferometer device is configured to be separated by a small distance .